T -KIT Model 1
056
Receiver Design Features:
0 Signetics
NE612
mixer-oscillator
0 True varactor tuning
(MV209)
0 Zener diode regulation
0
LM358
op amp bandpass
filter
0 Front-panel bandpass control
0 Signetics
TDA2611
A audio amplifier
IC
a Stereo jack
for
economical
"Walkman"
headphones
a Plenty
of
speaker audio
a Separate
"Bandset"
and "Bandspread" tuning controls
0
RF
gain control
a Provision
for
TX
sidetone injection
a Provision
for
receiver audio
muting
during
transmit
0 Frequency Counter
output
line
from
local oscillator
0 Efficient
6"WX2
~
"D
board
layout:
take your favorite ham band ANYWHERE!
a Jumper provision
for
separate
DC
supply
to
audio
IC
a Operates on
12-15
VDC .
Use
this
space (and page
4.),
to
plan
your
use
of
the T -KIT
1056
Direct
Conversion Receiver
Module
Board
Installing Parts
on
the
Circuit
Board:
When
we
say
"INSTALL"
a part,
we
mean:
0 Choose correct
part
value
0 Insert
in
correct
PC
Board
location
0 Insert correctly,
if
there is a
right
way
and
wrong
way
such as
for
the
transistor
and
LED
0 Solder all wires
or
pins
0 Trim
or
"nip"
excess
wire
lengths
1056-
6
Model 1
056
Circuit
Descrip-tion
I The Schematic Diagram is
printed
on pages
12-13.
~-~
The
efficient
'simplicity
of
this
and similar receivers is made
possible
by
the Signetics
NE612AN
mixer-oscillator, functionally
identical
to
the
well-known
NE602.
The
NE612AN
is used .
because
it
is standard TEN-TEC
inventory.
L 1,
C1
and C2 form a
tuned
RF
input
circuit
coupling
the
antenna
to
pins 1 and 2. The
dissimilar values
of
C 1 and C2 are selected
for
propBr impedance
matching. Potentiometer
R1
is an
attenuator
to
minimize
overload
by
strong signals and
nearby
AM
broadcasts, therefore
serving as
RF
gain
control.
The local
oscillator
frequency
is
determined
by
C3, C4, L2 (plus L3
on
80/75
and
160
meters),
plus the varactor
tuning
network
coupled
through
C5. Voltage
applied
through
tuning
pot
R2
and R4 ( 1
OOK)
to
the
MV209
varactor (D1) provides coarse
tuning
or
"band
set."
The fine-
tuning
or
"band spread"
by
R3 is done
by
coupling
the
control
voltage
to
D1
through
R5, 1
megohm.
As desired, changing the
value
of
R5
will
increase
or
decrease
the
fine-tuning
rate.
Zener diode D2
(6.2V)
regulates
the
voltage
to
the
oscillator's
varactor circuit,
supporting
U1
's
never-exceed Vee
limit
of
8V.
The
output
from pins 4 and 5
of
U1
is
low-level
audio,
the
direct-
conversion result
of
mixing
antenna
RF
input
with
the
variable
local oscillator frequency. This audio
output
is coupled
through
the
filter
network
formed
by
R6-R9 and
C1
0
to
the
inputs
of
op.-
amp U2a. The
LM358
IC (U2a,b) is a dual op-amp. The voltage
gain·
from
antenna
input
to
U 1
to
U2a
output
is
typically
68
dB.
The
other
LM358
op-amp (U2b) and
its
associated components
serve
as
an elementary bandpass
filter,
with
front-panel
filter
tuning done
by
potentiometer
R16.
The
output
of
U2b is coupled
through
C18
and
Volume/AF
Gain
Control R18
to
the
input
of
U3,
the
Signetics
TDA2611
A audio
amplifier IC, using
the
same general
circuitry
already proven in
TEN-TEC HF transceivers.
1056-
7
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